The variable overhead efficiency variance for January is:

A) $320 F
B) $316 U
C) $320 U
D) $316 F

Variable overhead efficiency variance measures the cost impact of the difference between actual and expected hours of input required to produce the actual output.

Variable overhead efficiency variance = (AH - SH) × SR

Where,

AH = Actual hours of input used
SH = Standard hours of input allowed for the actual output
SR = Standard rate per hour of the variable overhead cost

Given that,
AH = 7,800 hours
SH = 7,500 hours
SR = $4 per hour

Variable overhead efficiency variance = (7,800 - 7,500) × $4
= $1,200 U

Therefore, the correct option is C) $320 U.

SH = 8,700 units × 0.1 hours per unit = 870 hours
Variable overhead efficiency variance = (AH - SH)× SR
= (910 hours ? 870 hours)× $8.00 per hour
= (40 hours)× $8.00 per hour
= $320 U